THERE’S A dilemma growing this spring for growers and agronomists faced with controlling OSR disease, it emerged at this year’s Bayer CropScience Northern Disease Conference.

Dr Simon Oxley, SAC’s OSR expert, said growers face a conflicting position this season. He reckoned that azole rates will have to rise to get on top of both light leaf spot (LLS) but there is the danger that crops could be checked resulting in a detrimental impact on yields.

“LLS is the most damaging OSR disease for Scotland and the north of England. My concern is that with the first real winter for several years, I suspect we could see disease levels much higher than in previous seasons,” he told the meeting.

“To manage disease, it has been necessary to lift rates. However, over aggressive growth regulation could be a result of that.”

He is advising growers to use fungicides in sequence if practicable. “Proline (prothioconazole) is the best option we have with regard to LLS, but with autumn and spring use, growers could easily exceed the maximum recommended limit. It is important to protect azole chemistry, especially as we are starting to see some LLS isolates as being harder to control.

“Because it is the most active option we have Proline will be a key element in any spring programme, particularly at stem extension in high disease pressure situations, or as a first flowering spray for sclerotinia control in high risk crops.

“Other alternatives at stem extension in lower disease pressure situations which growers should consider include Folicur, Caramba or Punch C. The only concern I have is that Caramba is a particularly aggressive PGR so growers need to bear this in mind when planning programmes,” he said.

Alternatives to Proline at flowering include Filan for sclerotinia control. Amistar or Delsene 50 flo would be potential mixing partner fungicides at the sclerotinia timing depending on risk and timing.

Dr Oxley also suggested that when managing disease, Scottish and northern growers will need to take more account of varietal factors too. “Where markets allow, I would recommend growers select more resistant varieties. LLS can overcome a plant’s natural resistance quickly.”

Bayer’s Sean MacGill acknowledged delegates’ concerns over reliance on triazoles but suggested that they will be at the heart of OSR disease defence for some time to come.

“New chemistry is on the horizon but triazoles will be needed next season and beyond. It will be vital to protect what we have.”